- World Health Organization (WHO) announces that around 800 suspected cases of so-called swine flu have been recorded in Mexico, including 60 suspected deaths, as well as seven cases in the United States. Health authorities around the world go on alert.

Mexican officials later say the first recorded fatality was a 39-year-old woman who died on April 13 in Oaxaca, southeastern Mexico.

April 25

- WHO warns that the virus, identified as a member of the H1N1 family, has "pandemic potential." Mexico orders isolation of sick people and closes many public establishments.

April 27

- First three cases are confirmed in Europe.

- WHO raises its alert level from three to four on a scale of six, signaling a "significant increase in risk of a pandemic."

April 28

- First cases in central America and the Middle East.

April 29

- A 23-month-old Mexican child is the first confirmed death in the United States.

- WHO raises alert level to five, calling on countries to prepare for an "imminent" pandemic.

- The first cases involving people who had not visited Mexico are confirmed in the United States, Spain and Germany.